Along with the developments of civilian technologies of aviation, spaceflight, thermal power and etc, the demand on higher service temperature of the hot end parts of gas turbine engine is increasing. The superalloys and their single crystals are currently used at service temperatures approaching their upper limits of thermal stability. Under such a condition, from the viewpoint of improving material, the thermal barrier coating technique has been widely used as another feasible technique of reducing the surface working temperature of the vanes of the turbine engine.
The comparison research of National Aeronautics and Space Administration of USA indicated that the comprehensive properties of ZrO2 are relatively superior. ZrO2 has a thermal expansion coefficient of 11×10−6 K−1 nearest to that of the substrate alloy, while its thermal conductivity coefficient is only 2.1-2.2 Wm−1 K−1. Pure ZrO2, however, will undergo a martensitic transformation from tetragonal phase (t) to monoclinic phase (m) at normal service temperature. In order to make the coating acclimated to the high temperature thermal cycling working environment and to prolong the lifetime of the coating, small amount of stabilizer is generally added to ZrO2 to control and reduce the occurrence of such kind of transformation.
U.S. Pat. No. 5,789,330 (Kondo, et al.) disclosed a thermal barrier coating material obtained by doping ZrO2 with 0.1 wt %˜40 wt % of various phase stabilizers such as Y2O3, CaO, MgO, Sc2O3, rare earth oxides and the like. After being sintered, the amount of the monoclinic phase is 25˜75% of the system. The long-term maximum service temperature of the coating material was lower than 1200° C.
U.S. Pat. No. 6,231,991 disclosed that a material with pyrochlore structure, especially La2Zr2O7, could be used as a thermal barrier coating material. La2Zr2O7 has unique properties such as relatively low thermal conductivity and no phase transformation before melting. But the thermal expanse coefficient of La2Zr2O7 is lower than that of YSZ. The difference between the thermal expanse coefficient of La2Zr2O7 and that of substrate alloy is bigger. The occurrence of internal stress in the coating due to mismatch of thermal expansion at high temperature will be more serious. As a result, cycling life of the coated layer is short.